Aqueous dispersion of high molecular weight polyester for chip resistant primer

ABSTRACT

The present invention is directed to an aqueous dispersion of a polyester salt and polymeric vehicles which include the aqueous dispersions of a polyester salt. The polymeric vehicle is particularly effective for providing coating binders in cured primer coatings. The primer coating compositions are useful for multilayer paint coating films which have at least two layers of paint film including the cured primer coating composition film. The use of the primer polymeric vehicles of the present invention in conjunction with one or more additional overlaying top coating film layers provide a multiple layer coatings having improved adhesion and chip resistance.

[0001] The present application is a continuation-in-part application ofU.S. Ser. No. 09/161,145 filed Sep. 25, 1998 and of U.S. Ser. No.09/160,843 filed Sep. 25, 1998.

[0002] The present invention relates to stable aqueous polyesterdispersions useful as primers. More particularly, the aqueous polyesterdispersions balance relatively high molecular weights and low hydroxylnumbers to provide a primer coating that effectively improves chipresistance of paint coatings overlaying the primer while maintainingadhesion and low levels of volatile organic compounds and lowviscosities.

BACKGROUND OF THE INVENTION

[0003] Automotive and other durable coatings are complex multilayersystems which rely on certain performance criteria at each level foroverall success. The bulk of the responsibility for providing improvedchip resistance lies with the primer surface layer. However, improvingchip resistance properties of automotive coatings or other types ofprotective or decorative durable coatings is clearly a system-dependenttask. For many systems, there appears to be several key ingredients toachieving incremental improvements. A chip-resistance test is by naturehigh in stress, impact, and shear, which intuitively generateshypotheses based on the softness, or rubber-like characteristics of theprimer layer. Any contributions from the primer to increase brittlenesseventually may lead to reduced chip performance. This can be related tothe degree of cross linking. Very low and very high levels of crosslinking in such systems lead to poor chip resistance. In the case of lowcross linking, the coating does not possess the strength propertiesnecessary to withstand the impact and shear forces applied by thegravel. The base molecular weight is usually too low to provideappropriate elastic properties associated with light cross linking. Theresult is flow and scission on gravel impact. An extremely high crosslink density affords large numbers of covalent cross links which impartbrittleness to the coating, and failure is based on the inability of thecoating to absorb and evenly distribute these concentrated forcesapplied at the gravel impact. The material neither flows, norelastically deforms, but instead suffers brittle fracture. Further,cross linkers often cause VOCs by virtue of VOC by product release fromthe cross link reaction between the cross linkers and polymeric resin.Also complicating systems which use separate cross linking agents is thepropensity for the cross linking agent to react with itself. Forexample, self-condensation of melamine cross linkers is a potentialcompeting reaction, which may result in local areas of highconcentration of highly cross linked melamine resin. This would producelocalized brittleness which may result in chip or adhesion failures.Another key contributor to successful chip resistance is the adhesion ofthe primer to the substrate, and the subsequent adhesion of anotherpaint coating to the primer (collectively intercoat adhesion). A majorcontributor to this effect is the functionality of the primerresin-polar group functionality including hydroxyl and carboxyl thatplay a key role in interactions with the substrate and other paintlayers.

[0004] In order to obtain the optimal chip-resistant properties, thecoatings overlying the primer and the primer base resin must eachdeliver a balance of properties to the final coating. The easiest way tomaximize mechanical properties of the primer resin is to increasemolecular weight. Increases in molecular weight, however, generallyincrease the viscosity of such resins. While high viscosity resins maybe cut with organic solvents, this results in an undesirable increase involatile organic compounds (VOCs).

SUMMARY OF THE INVENTION

[0005] The present invention is directed to an aqueous dispersion of apolyester salt and polymeric vehicles which include the aqueousdispersions of a polyester salt. The polymeric vehicle is particularlyeffective for providing coating binders in cured primer coatings (thecured primer paint coating film). The primer coating compositions (alsoknown as formulated coating compositions) are useful for multilayerpaint coating films which have at least two layers of paint filmincluding the cured primer coating composition film. The use of theprimer polymeric vehicles of the present invention in conjunction withone or more additional overlaying top coating film layers provide amultiple layer coating system having improved adhesion and chipresistance.

[0006] The primer polymeric vehicle of the invention permits the use ofless cross linker to cross link the polyester salt. The use of lesscross linker results in the release of less VOCs upon cross linking anda lower cross linker density in the cured coating binder film of in thecured primer coating composition. The reduced cross link density withthe relative high molecular weight of the polyester salt providesimproved chip resistance. While not intending to be bound by a theory,the polyester salt of the present invention has a higher molecularweight which enhances chip resistance and needs less cross linker (whichalso enhances chip resistance) to cure into a useable film than apolyester which is compositionally the same (and is not a metal orammonium salt), but has a lower molecular weight. These lower molecularweight polymers are used in high solids systems and are dispersed in anorganic solvent or mixed organic/water solvent system. Moreover, themolecular weight of the polyester in the latter high solids system cannot be increased without also increasing the viscosity of the polymerdispersion or solution (increasing molecular weight inherently increasesviscosity in such systems). Hence, the polymeric vehicle of the presentinvention includes a water dispersible polyester salt having uniquecombination of high molecular weight, a relatively low hydroxyl value ornumber, a unique ratio of hydroxyl value to number average molecularweight and a polyester with an acid value which permits formation of thewater dispersible salt.

[0007] The polyester salt is cross linkable to form a cured coatingbinder in a primer paint coating film which is chip resistant when it ispart of a multilayer paint coating system which has at least two paintfilm layers including the cured primer paint coating film layer. Thecured coating binder of the primer of the invention also renders themultilayer paint coating system chip resistant. Hence, the polymericvehicle of the primer coating composition balances the hydroxyl valueand number average molecular weight of the polyester salt in the aqueousdispersion to provide VOC reduction through the use of an aqueous systemwith reduced amount of cross linker as well as improved chip resistanceand adhesion for the cured primer paint coating film of the primercoating composition.

[0008] For enhancing chip resistance of coatings systems in whichprimers of the invention are used, the desired hydroxyl number isgenerally inversely related to the polyester molecular weight. By way ofexample, the polymeric vehicle for the primer coating composition orformulated coating comprises an aqueous dispersion of a polyester saltwhich is the residue of a polyester having a number average molecularweight of about 1500 Daltons and a hydroxyl value of about 90. In suchaspect, the polyester has a hydroxyl equivalent weight of about 600.This aqueous dispersion is effective for providing the polymeric vehiclewith less than about 5 weight percent organic solvent. At a highermolecular weight, the polymeric vehicle for the primer coatingcomposition or formulated coating comprises an aqueous dispersion of apolyester salt which is the residue of a polyester having a numberaverage molecular weight of about 2800 Daltons and a hydroxyl value ofabout 50. In such aspect, the polyester has a hydroxyl equivalent weightof about 1100. This aqueous dispersion is effective for providing thepolymeric vehicle with less than about 5 weight percent organic solvent.

[0009] The chip resistance of the multilayer paint coating system whichincludes the coating binder of the primer of the invention, is superiorto the chip resistance of a multilayer paint coating system whichincludes a primer which has compositionally the same polyester which hasa lower molecular weight and is not a salt. It is these latter lowermolecular weight polyesters which are generally used with organicsolvent or mixed organic/water solvent systems. They are high in VOCsand generally require more cross linker to cure than the polymericvehicle of the present invention.

[0010] In an important aspect of the invention, the polymeric vehiclefor the primer coating composition or formulated coating comprises anaqueous dispersion of a polyester salt which is the residue of apolyester having a number average molecular weight of at least 1500Daltons and a hydroxyl value of not more than 90. In one aspect, thepolyester has a hydroxyl equivalent weight of about 600 to about 1100.This aqueous dispersion is effective for providing the polymeric vehiclewith less than about 5 weight percent organic solvent. In anotherimportant aspect, the salt of the polyester in the aqueous dispersionhas a particle size of less than 400 nm.

[0011] In yet another aspect, the polyester salt is the residue of apolyester having an acid value of at least 30, and in an importantaspect, from about 40 to about 50, the polyester salt having a hydroxylvalue of from about 90 to about 50 and the salt having a number averagemolecular weight of from about 1500 to about 2800 Daltons (not includingthe cationic portion of the salt, that is the salt includes the residueof a polyester where the polyester has a molecular weight of from about1500 to about 2800 Daltons). The polymeric vehicle of the invention iseffective for providing a multilayer paint coating system and primercoating binder with a two pint chip number rating of at least about 5and a two pint chip size of at least about A (using the Society ofAutomotive Engineers Chip Test No. J400) when the polymeric vehicle ofthe primer is cured and a part of a multilayer paint coating system ofat least two layers inclusive of the primer coating binder. Despite theuse of a relatively high molecular weight polyester, the polymericvehicle and the aqueous dispersion of the present invention have aviscosity of less than about 10 poise at a temperature of about 25° C.using less than about 5 weight percent organic solvent, and in animportant aspect, less than about 2 weight percent organic solvent.

[0012] As previously stated above, the polyester salt requires lessequivalent amounts of cross linker for cross linking than the same lowerweight polyester (which is not a salt) having molecular weights of lessthan about 1500 Daltons, which polyester is generally less than about800 Daltons. Suitable cross linkers include multifunctional amino resinsand blocked isocyanate compounds. The polymeric vehicles of theinvention generally will include from about 15 to about 25 weightpercent crosslinker, based on the weight of the polymeric vehicle.Polymeric vehicles which use the low molecular weight polyesterspreviously described are polyesters which are not salts and which areused in high solids systems will generally require from about 35 toabout 50 weight percent crosslinker.

[0013] In accordance with the present invention, an ionic functionalpolyester polymer is synthesized neat and subsequently mixed withhydrophilic organic solvent. The aqueous polymer dispersion is made byforming a polyester having sufficient ionizable groups to provide thepolyester with an acid value of from about 30 to about 50. The polymerhas a solubility in the hydrophilic solvent of at least about 50 weightpercent, and the organic hydrophilic solvent has a solubility in waterof at least about 5 weight percent. As previously stated, the polyesterprior to neutralization reactions to form a salt, has a number averagemolecular weight of at. least about 1500, and in an important aspect,about 1500 to about 2800 and a hydroxyl number of from about 50 to about90. At least about 30 percent of the ionizable groups of the polyesterpolymer in the solvent are neutralized with an amount of neutralizereffective to form a solution of neutralized polymer salt. Thereafter thesolution of neutralized polymer salt is mixed with water to form a blendof water/organic solvent/neutralized polymer. The organic solvent thenis stripped from the latter blend at not more than about 65° C. to forma dispersion of neutralized polymer salt in water. This dispersion has aviscosity of less than about 10 poise at a temperature of about 25° C.The neutralizer may be any salt-forming base compatible with theionizable functional polymer such as sodium hydroxide or an amine. In avery important aspect the neutralizer is an amine type which is selectedfrom the group consisting of ammonia, triethanol amine, dimethyl ethanolamine, and 2-amino-2-methyl-1-propanol. Not all of the ionizable groupson the polymers need to be reacted with the base (or neutralized).

[0014] Depending on the type of ionizable groups present in the polymerit may be important that the polymer is neutralized before it is blendedwith water so that water dispersible neutralized ionizable groups aregenerally evenly distributed throughout the polymer. It is alsoimportant that the organic solvent and some water are removed orstripped from the blend at a duration, temperature and pressureeffective for providing an aqueous dispersion having a resin meanparticle size of not greater than about 400 nm. In an important aspectthe the polymer salt concentration is at least about 30 weight percent,the organic solvent concentration of less than 5 weight percent, andeven less than 2 weight percent. In an important aspect, where theneutralizer is an amine or ammonia, the mean particle size of the resinis maintained with a stripping temperature of not more than about 65° C.at a pressure which permits such a stripping temperature.

[0015] In another aspect, the invention provides formulated coatingsthat include aqueous polymer dispersions of the invention withco-solvents selected from the group consisting of butoxy ethanol,diethylene glycol monobutyl ether, secondary butyl alcohol, propyleneglycol n-butyl ether, dipropylene glycol n-butyl ether, propylene glycoln-propyl ether, propylene glycol t-butyl ether, and mixtures thereof.These formulated coating compositions generally will include rheologymodifiers such as fumed silica and bentonite clays.

DETAILED DESCRIPTION Definitions

[0016] “Hydroxyl number” or “hydroxyl value” which is also called“acetyl value” is a number which indicates the extent to which asubstance may be acetylated; it is the number of milligrams of potassiumhydroxide required for neutralization of the acetic acid liberated onsaponifying 1 g of acetylated sample. For purposes of this application,hydroxyl number is based on solid polyester in the system and not onsolution.

[0017] “Hydroxyl equivalent weight” is calculated from the hydroxylnumber (OHN) per ASTM D1957 as follows.

[0018] Hydroxyl Equivalent Weight=56,100/OHN

[0019] The hydroxyl number units are mg KOH/gram of resin solids.

[0020] “Polymeric vehicle” means all polymeric and resinous componentsin the formulated coating, i.e., before film formation, including butnot limited to the water dispersible salt of a polymer. The polymericvehicle may include a cross linking agent.

[0021] “Coating binder” means the polymeric part of the film of thecoating after solvent has evaporated and after crosslinking.

[0022] “Formulated coating composition” means the polymeric vehicle andsolvents, pigments, catalysts and additives which may optionally beadded to impart desirable application characteristics to the formulatedcoating and desirable properties such as opacity and color to the film.

[0023] The term “aqueous medium” as used herein means water and amixture of water and hydrophilic organic solvent in which the content ofwater is at least 10% by weight. Examples of hydrophilic solventsinclude alkylalcohols such as isopropanol, methanol, ethanol,n-propanol, n-butanol, secondary butanol, tert-butanol and isobutanol,ether alcohols such as methyl cellosolve, ethyl cellosolve, propylcellosolve, butyl cellosolve, methyl carbitol and ethyl carbitol, etheresters such as methyl cellosolve acetate and ethyl cellosolve acetate,dioxane, dimethylformamide, diacetone alcohol, methyl ethyl ketone,acetone, and tetrahydrofurfuryl alcohol.

[0024] “Ionizable group” refers to functional groups on the polymer thateffect water dispersibility of the polymer. An example of an ionizablegroup includes —COOH.

[0025] “Neutralizer” refers to compositions which can react withionizable groups on the polymer to affect water dispersibility. Examplesof neutralizers useful in the present invention include amines, ammonia,and metal hydroxides including NaOH and KOH. In an important aspect ofthe invention, the neutralizers are amines and ammonia.

[0026] “Residue of a polyester salt” refers to the reaction product ofan ionizable polyester with a neutralizer.

[0027] “Cross linker” or “cross linking agent” means a polyfunctionalcompound capable of reaction with a hydroxyl of a polyol or a phenolhydroxyl or both. These agents include a compound having di- orpolyfunctional isocyanate groups or a polyfunctional amino resin. Theisocyanate compound or amino resin contains isocyanate or other crosslinking functional groups that are capable of forming covalent bondswith hydroxyl groups that are present on the polyester polyol in thepolymeric vehicle. The cross linking agent may be a blend; hence, theremay be more than one substance which forms a blend of substances whichform covalent bonds with the hydroxyl groups of the polyester polyol.Amino reins and polyisocyanates are such cross linking agents.

[0028] “Isocyanate compound” means a compound which when reacted with anhydroxyl results in a carbamate linkage. The isocyanate compound may bea blocked polyisocyanate, a blocked biuret, a blocked uretdione and ablocked isocyanurate.

[0029] Diisocyanates which may be used in the invention additional toHDI include isophorone diisocyanate (IPDI), tetramethylxylenediisocyanate (TMXDI), and other aliphatic diisocyanates such astrimethylene diisocyanate, tetramethylene diisocyanate, pentamethylenediisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate,1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylenediisocyanate; cycloalkylene diisocyanates such as1,3-cyclopentane-diisocyanate, 1,4-cyclohexane-diisocyanate and1,3-cyclohexane-diisocyanate; and aromatic diisocyanates such asm-phenylene diisocyanate, p-phenylene diisocyanate,4,4′-diphenyldiisocyanate, 1,5-naphthalene diisocyanate,4,4′-diphenylmethane diisocyanate, 2,4- or 2,6-tolulene diisocyanate.

[0030] “Polyisocyanate” can mean compounds with two or more isocyanategroups [—N═C═O] which compounds may be biurets and isocyanurates. Thepolyisocyanates may be dimerized or trimerized diisocyanates such astrimerized HDI or IPDI and triisocyanates such astriphenylmethane-4,4′,4″-triisocyanate, 1,3,5-triisocyanatobenzene,1,3,5-triisocyanatocyclohexane, 2,4,6-triisocyanatotoluene andω-isocyanatoethyl-2,6-diisocyanatocaproate; and tetraisocyanates, suchas 4,4′-diphenyldimethylmethane-2,2′,5,5′-tetraisocyanate.

[0031] “Carbamate linkage” means —OC(═O)N(—H)— which can be a urethanelinkage.

[0032] “Biuret” means an isocyanate reacted with water in a ratio ofthree equivalents of isocyanate to one mole of water, such as the biuretof HDI shown below:

[0033] An “isocyanurate” is a six-membered ring having nitrogens at the1, 3 and 5 positions and keto groups at the 2, 4 and 6 positions, thenitrogens being substituted with an isocyanate group, such as shownbelow in the isocyanurate of HDI.

[0034] Methylol (alkoxymethyl) amino crosslinking agents are suitablefor use in the present invention and are well known commercial products,and are generally made by the reaction of di (poly) amide (amine)compounds with formaldehyde and, optionally, a lower alcohol.

[0035] “Aminio resins” includes melamine resins amd may also be referredto as “melamine-formaldehyde resins” or “alcoholatedmelamine-formaldehyde resin.” Examples of suitable amino-crosslinkingresins include one or a mixture of the following materials:

[0036] Melamine Based Resins:

[0037] wherein R is the following:

[0038] R=CH₂, (Cymel)® 300, 301, 303);

[0039] R=CH₂, C₂H₅ (Cymel® 1116);

[0040] R=CH₂, C₂H₅ (Cymel® 1130, 1133)

[0041] R=C₂H₅ (Cymel 1156) ; or

[0042] R=CH₂, H (Cymel® 370, 373, 380, 385).

[0043] The preferred melamine is hexamethoxymethyl melamine.

[0044] Benzoquanamine Based Resins:

[0045] wherein R=CH₃, C₂H₅ (Cymel® 1123).

[0046] Urea Based Resins:

[0047] wherein:

[0048] R=CH₃, H (Beetle™ 60, Beetle™ 65); or

[0049] R=C₂H₅ (Beetle™ 80).

[0050] Gycoluryl Based Resins:

[0051] wherein:

[0052] R=CH₃, C₂H₅ (Cymel® 1171); or

[0053] R=C₂H₅ (Cymel® 1170).

[0054] “Polyester” means a polymer which has

[0055] linkages in the main chain of the polymer.

[0056] As used herein, the reaction product of an alkali metal base oramine or ammonia with a carboxyl group or other ionizable group which ispart of a polyester produces a “salt”.

[0057] “Substantially solventless” means a polymeric vehicle orformulated coating composition having not more than about five weightpercent organic solvent.

[0058] “Solvent” means an organic solvent.

[0059] “Organic solvent” means a liquid which includes but is notlimited to carbon and hydrogen which liquid has a boiling point in therange of not more than about 150° C. at about one atmosphere pressure.

[0060] “Hydrophilic solvent” means a solvent that has a solubility inwater of at least about 5 weight percent at room temperature.

[0061] “Volatile organic compounds” (VOCs) are defined by the U.S.Environmental Protection Agency at 40 C.F.R. 51.000 of the FederalRegulations of the United States of America.

[0062] A “high solids” or “high solids formulated coating composition”means an aqueous formulated coating composition containing more thanabout 30 weight percent solids, and in an important aspect of thepresent invention about 35 weight percent to about 70 weight percentsolids as per ASTM test D-2369-92. “Film” is formed by application ofthe formulated coating composition to a base or substrate, evaporationof solvent, if present, and cross-linking if necessary.

[0063] “Baked formulated coating composition” means a formulated coatingcomposition that provides optimum film properties upon heating or bakingabove ambient temperature.

[0064] “Dispersion” in respect to a polymeric vehicle, formulatedcoating composition, or components thereof means that the compositionmust include a liquid and particles detectable by light scattering.

[0065] “Dissolved” in respect to a polymeric vehicle, formulated coatingcomposition or components thereof means that the material which isdissolved does not exist in a liquid in particulate form where particleslarger than single molecules are detectable by light scattering.

[0066] “Soluble” means a liquid or solid that can be partially or fullydissolved in a liquid. “Miscible” means liquids with mutual solubility.“Imbibe water” means a liquid is miscible with water.

[0067] “Acid number” or “acid value” means the number of milligrams ofpotassium hydroxide required for neutralization of or reaction withionizable groups present in 1 g of material, such as resin.

[0068] “Substantially free of emulsifier” means a composition with notmore than about 0.5 weight percent emulsifiers. Aqueous dispersions ofthe present invention are substantially free of emulsifier.

[0069] As used herein the term “inversion” refers to a phase changewhere a mobile phase becomes a disperse phase. For example, an inversiontakes place where sufficient oil is added to an oil in water phase suchthat phases invert to change from a oil in water phase to a water in oilphase. Conversely, in an “inversionless” system, the mobile phase doesnot become the disperse phase and the corresponding increase inviscosity associated with dispersions does not occur. In an importantaspect of the present invention, the viscosity of the system duringprocessing remains less than about 20 poise, and in a very importantaspect, less than about 10 poise at 25° C.

Stage One: Preparation of Polyester

[0070] In accordance with stage one of the present invention, apolyester polymer is synthesized neat and subsequently blended into anorganic hydrophilic solvent which has limited to infinite solubility inwater. Polyester polymers useful in the present invention include thosethat provide a polyester salt where the polyester salt is the residue ofa polyester having a number average molecular weight of from about 1,500to about 2,800 Daltons. In an important aspect of the invention, thepolyester polymers have an acid value of less than about 50, and in avery important aspect, about 30 to about 50.

[0071] The polyesters used herein are reaction products of polyhydricalcohols and polycarboxylic acids. Examples of suitable polyhydricalcohols include triols and tetraols such as trimethylolpropane,trimethylolethane, tris(hydroxyethyl) isocyanurate, glycerine, andpentaerythritol, and dihydric alcohols or diols that may includeneopentyl glycol, dimethylol hydantoin, ethylene glycol, propyleneglycol, 1,3-butylene glycol, diethylene glycol, dipropylene glycol,1,4-cyclohexane dimethanol, Esterdiol 204 (trademark of Union Carbide),1,3-propane diol, 1,6-hexanediol, and dimethylol propionic acid (DMPA).As can be seen from the reference to DMPA, polyhydric alcohols may have—COOH groups.

[0072] Carboxylic acids utilized in the invention may be aromaticcarboxylic acids such as isophthalic acid, terephthalic acid, phthalicacid, phthalic anhydride, dimethyl terephthalic acid, naphthalenedecarboxylate, tetrachlorophthalic acid, terephthalic acid bisglycolester, and benzophenone dicarboxylic acid; and cycloaliphatic, aliphaticcarboxylic acids, and polyacids such as trimellitic anhydride (TMA). Ascan be seen from the reference to TMA, diacids may have additional —COOHgroups.

[0073] In another important aspect of the invention, the polyesterpolymers that are synthesized neat are blended with a solvent selectedfrom the group consisting of alkylalcohols such as isopropanol,methanol, ethanol, n-propanol, n-butanol, secondary butanol,tert-butanol and isobutanol, ether alcohols such as methyl cellosolve,ethyl cellosolve, propyl cellosolve, butyl cellosolve, methyl carbitoland ethyl carbitol, ether esters such as methyl cellosolve acetate andethyl cellosolve acetate, dioxane, dimethylformamide, diacetone alcohol,methyl ethyl ketone, acetone, and tetrahydrofurfuryl alcohol. Thepolymers of the invention have a solubility at processing temperaturesin the hydrophilic solvent of at least about 50 weight percent, morepreferably at least about 80 weight percent, based on the total weightof the composition.

[0074] Stage one provides a resin in a hydrophilic solvent which can bestored, and which can be further processed in stage two. In an importantaspect, the resin provided in stage one has a storage stability of atleast about 6 months.

Stage Two: Polyester Dispersion

[0075] Neutralizing the Resin

[0076] The polyester salt is formed in situ in the organic solvent withwater being mixed with the polyester salt/organic solvent combination.In accordance with the invention, neutralizer is added to an organicsolvent solution containing the polyester in an amount effective forneutralizing the polyester to provide sufficient salt to render thepolyester dispersible in water. Neutralizer useful in the presentinvention include but are not limited to ammonia, triethanol amine,dimethyl ethanol amine, 2-amino-2-methyl-1-propanol, NaOH and KOH.

[0077] The amount of neutralizer added is dependent on acid value andmolecular weight. In one aspect, from about 30 to about 100 percent ofthe carboxyl groups are neutralized to obtain the solids level and lowVOC level of the dispersions of the invention. In another aspect,neutralizer is mixed with the polyester polymer in an amount effectiveto provide at least about 70 parts polymer salt in less than about 30parts solvent wherein with subsequent mixing with water, the neutralizedpolymer will provide a dispersion which comprises not more than about 70weight percent water, based on the weight of the dispersion.

[0078] In a very important aspect of the invention, where the ionizablegroup is carboxyl, the polyester requires about 70% to about 100%neutralization to stabilize the dispersion. In another important aspectof the invention, the process provides a mean particle size of not morethan about 400 nm, with a typical mean particle size in the range ofabout 40 nm to about 200 nm as measured by laser light scattering.

[0079] The polyester polymer can be preneutralized by making the polymerwith metal, amine or ammonia salts of the ionizable groups such as—COOH. The polymer made from these “preneutralized” monomers would havean acid value, as measured by titration, of at least about 30 if theionizable groups which form part of the polymer were not alreadyneutralized. In this aspect of the invention, monomers have apolyfunctionality such as a difunctionality which permits them to formpolymers that also have the salt form of the ionizable groups.

[0080] An example of such a monomer is

[0081] where A and B are —OH and/or —COOH which can form a polyester ina condensation reaction and C is —COOX, where X is an alkali metal suchas sodium or potassium.

[0082] Addition of Water

[0083] In the next step of stage two of the process, water having atemperature of about 25° C. to about 65° C. is added to the neutralizedresin solution. Lower temperatures provide smaller mean particle sizes.

[0084] In an important aspect of the invention, the initial ratio ofsolvent to water (solvent/water) is from about 0.15 to about 0.45 forpolyester polymer. The initial ratio of solvent to water is important toensure that inversion does not take place during subsequent stripping ofsolvent. The amount of water to be added may be greater than thatrequired to obtain the desired solids of the final dispersion. Somewater loss typically occurs during solvent distillation. The systemrequires sufficient solvent at the beginning to solubilize the saltprior to water addition.

[0085] In an alternative aspect of the invention, polymer in hydrophilicsolvent is added to water that already contains a neutralizer.

[0086] Removal of Solvent

[0087] In the next step of the process, the organic solvent and water ifrequired are removed or stripped from the neutralizedresin/water/solvent mixture. A reduced atmospheric pressure may beapplied to the mixture to aid in the removal of solvent and water. In animportant aspect, vacuum may range from about 22 inches to about 29inches of mercury gauge. With lower temperatures, a higher vacuum mustbe used to remove solvent. Lower reaction temperatures result in lessfoaming, as the higher vacuum coupled with the surface tension of thebubbles helps to break the bubbles. In another aspect of the invention,solvent/water is stripped with heat being supplied through the use of aheat exchanger. Use of a heat exchanger may reduce distillation timesand temperatures and further minimize destruction of the salt.

[0088] In a very important aspect of the invention, solids levels of atleast about 30 weight percent to about 45 weight percent can be attainedfor polyesters.

[0089] In another aspect of the invention, solvent that is removed canbe purified and reused. A simple flash or multiple stage distillation issufficient to clean the solvent of any contamination.

[0090] In an alternative aspect, the invention permits manufacture ofthe water dispersion from the polymer using one reaction vessel. Thewater dispersion of the invention does not require emulsifying agentsand does not have more than about 2 weight percent, based on the weightof the composition, of organic solvent after the distillation of thesolvent. In an important aspect, the aqueous dispersion contains fromabout 0.2 to about 2 weight percent organic solvent.

[0091] The water dispersion of the invention includes the waterdispersible amine salt of the polymer as well as the unsalified polymer,but in the aspect of the invention where the ionizable group is acarboxyl, the aqueous dispersion of the invention does not have lessthan 30 percent of the free carboxyl groups of the polymer neutralizedor converted into a salt. As the acid number of the polymer goes down,the higher the percent of the carboxyl groups on the polymer must beneutralized. Where the ionizable groups are —COOH, to maintain thedispersion below an acid value of about 15, about 100% of the carboxylgroups on the polymer should be neutralized to the salt. In an importantaspect of the invention, about 100% of the carboxyl groups on thepolymer are neutralized to the salt and the dispersions of the inventiondo not have more than about 1 pound per gallon of dispersion (120 g/l)VOCs, and in a very important aspect the dispersion has about 0.2 poundsper gallon of dispersion VOCs. The water dispersion of the inventionwith about 0.2 pounds per gallon VOC is stable through at least about 1freeze-thaw cycle, and up to about 4 freeze-thaw cycles. Freeze-thawcycles can be increased with small amounts of solvents or glycols as istypically used for latex systems.

Formulated Coating Compositions

[0092] The polymeric vehicle is incorporated into a formulated coatingcomposition which upon heating provides a baked formulated coatingcomposition or cured composition. Baking is above ambient temperatureswith a cross linker to provide a coating binder. The polymeric vehiclewhich includes the water dispersion of the invention provides aformulated coating composition having VOCs of less than 1 pound pergallon of formulated coating composition, includes water dispersiblepolymers and salts thereof having the above indicated molecular weightsand not only eliminates a need for, but is substantially free ofemulsifiers, surfactants and coalescents.

[0093] Water dispersion of such high molecular weight polymers provide acoating binder and baked formulated coating compositions with improvedfilm performance characteristics which include, but are not limited toimproved chip resistance, adhesion which is just as good as lowermolecular weight higher VOC systems, improved lay down performance ofthe wet film, enhanced film build of the film per pass, faster drytimes, improved corrosion resistant films per pass, improved corrosionresistant films, harder films, more abrasion resistant films, andimproved humidity resistant films. The polymeric vehicle of theinvention also provides coating binders for improved exterior“ultraviolet resistant” durable films which are derived from an aqueouslow VOC formulated coating composition. Films provided from theinvention are improved over that of aqueous thermoplastic emulsions orwater reducible systems of low molecular weight thermoplastic or thosethermosetting polymers requiring cross linking.

[0094] The following examples illustrate methods for carrying out theinvention and should be understood to be illustrative of, but notlimiting upon, the scope of the invention which is defined in theappended claims.

EXAMPLES Example 1 Polyester Dispersion

[0095] A. Synthesis of Polyester Polymer:

[0096] 1. 218.9 grams of neopentyl glycol (NPG), 77.2 grams oftrimethylol propane (TMP), and 248.4 grams of 1,6-hexanediol (HDO) werecharged to a round bottom flask equipped with a packed column, partialcondenser, receiver, and nitrogen blanket.

[0097] 2. The flask was heated until the glycols were melted and 322.8grams of Adipic acid (AA) and 322.8 grams of Isophthalic acid (IPtA)were added with mixing.

[0098] 3. The temperature was steadily and gradually increased to 220degrees centigrade and waters of esterification were removed.

[0099] 4. When the acid value was 6.8, the temperature was reduced to170 degrees centigrade.

[0100] 5. 80 grams of trimellitic anhydride (TMA) was added to the flaskand the temperature was maintained at 170 degrees centigrade.

[0101] 6. Waters of esterification were removed until an acid value of46.3 was reached.

[0102] 7. The temperature was reduced to 90 degrees centigrade and thepolymer was cut with methyl ethyl ketone (MEK).

[0103] Properties of the Polyester Solution: Percent Solids (NVM) 70Acid Value (Mg KOH/g) 45 Molecular Weight (Mn) 2350 Hydroxy number (MgKOH/g) 65

[0104] B. Preparation of Polyester Dispersion:

[0105] 1. 635 grams of the polyester solution in MEK and 26.4 grams ofAMP-95 were charged to a round bottom flask equipped with a totalcondenser and receiver.

[0106] 2. The flask was heated to 40 degrees centigrade with mixing.

[0107] 3. Upon reaching temperature, 666 grams of deionized water wasadded over approximately 30 minutes.

[0108] 4. Vacuum was applied to the flask and slowly increased to amaximum of 26 inches of mercury.

[0109] 5. Vacuum was continued until the desired percent solids of thedispersion was reached.

[0110] 6. After the desired amount of distillate was removed, the vacuumwas broken and the resulting product analyzed.

[0111] Properties of the Polyester Dispersion: Percent Solids (NVM) 41.0Viscosity (cps) 45 pH (units) 6.0 particle size (nm) <80 weight/gal(lbs) 8.9

Example 2 Polyester Dispersion

[0112] A. Synthesis of Polyester Polymer:

[0113] 1. 1170.0 grams of nenopentyl glycol (NPG), 412.5 grams oftrimethyol propane (TMP), and 1687.5 grams of butyl-ethyl-propanediol(BEPD) were charged to a round bottom flask equipped with a packedcolumn, partial condenser, receiver, and nitrogen blanket.

[0114] 2. The flask was heated until the glycols were melted, and 1725.0grams of Adipic acid (AA) and 1725.0 grams of Isophthalic acid (IPtA)were added with mixing.

[0115] 3. The temperature was steadily and gradually increased to 220degrees Celsius and waters of esterification were removed.

[0116] 4. When the acid value was 3.1, the temperature was reduced to170 degrees celsius.

[0117] 5. 427.5 grams of trimellitic anhydride (TMA) was added to theflask and the temperature was maintained at 170 degrees celsius.

[0118] 6. Waters of esterification were removed until an acid value of41.2 was reached.

[0119] 7. The temperature was reduced to 90 degrees centigrade and thepolymer was cut with isopropyl alcohol (IPA).

[0120] Properties of the Polyester Solution: Percent Solids (NVM) 69.4Acid Value (Mg KOH/g) 41.1 Molecular Weight (Mn) 2050 Hydroxyl number(mg KOH/g) 65

[0121] B. Preparation of Polyester Dispersion:

[0122] 1. 1352 grams of the polyester solution in IPA and 26.4 grams ofN,N-dimethylethanolamine (DMEA) were charged to a round bottom flaskequipped with a total condenser and receiver.

[0123] 2. The flask was heated to 40 degrees Celsius with mixing.

[0124] 3. Upon reaching temperature, 1476 grams of deionized water wasadded over approximately 30 minutes.

[0125] 4. Vacuum was applied to the flask and slowly increased to amaximum of 26 inches of mercury.

[0126] 5. Vacuum was continued until the desired percent solids of thedispersion was reached.

[0127] 6. After the desired amount of distillate was removed, the vacuumwas broken and the resulting product analyzed.

[0128] Properties of the Polyester Dispersion: Percent Solids (NVM) 42.6Viscosity (cps) 45 pH (units) 7.0 particle size (nm) <80 weight/gal(lbs) 8.9

Example 3 Paint Formulation with a Polyester Dispersion

[0129] Preparation of Paint:

[0130] The dispersed polyester from Example 1 was formulated into aprimer as follows:

[0131] 1. A 228 gram aliquot of resin dispersion prepared as describedin Example 1 was placed in a one liter stainless steel mixing vessel.

[0132] 2. 9 grams of propylene glycol monobutyl ether and 36 grams ofdeionized water were then added to the resin dispersion

[0133] 3. A vertical disperser was then inserted.

[0134] 4. 195 grams of TiO2 (R-960, DuPont) and 5 grams of Raven 16 wereadded under agitation.

[0135] 5. Approximately 300 grams of 3 mm glass beads were added to thevessel, and the mixture was dispersed at high speed for 30 minutes todisperse the pigment to a 7 Hegman.

[0136] 6. The mill was slowed to mixing speed, and the following letdown ingredients were added under slow agitation:

[0137] 143 grams of polyester dispersion

[0138] 40 grams of Cymel 301

[0139] 7.2 grams of Nacure 3525

[0140] 0.5 grams of Surfynol 104BC

[0141] 7. After incorporation of these ingredients, the mixture wasfiltered through a 25 micron filter cone to remove the glass beads. ThepH then adjusted to 8.2 to 8.5 with AMP-95, and then reduced to 34-36seconds #4 Ford cup with deionized water.

[0142] The resulting paint had a calculated VOC of less than 2.0 poundsper gallon and 51% weight non-volatile.

[0143] Properties of the Paint:

[0144] The formulated paint was tested by spraying onto high edgeprotection electrodeposition coated galvanized steel panels. Filmthickness of the primer was 1.0 mil dry. The painted panel was flashedat room temperature for 5 minutes, and then flashed an additional 10minutes in 180 degrees F. oven. The painted panel was baked 25 minutesat 330 degrees F. The top three inches of the panel was masked off andthe panel was then top coated with a commercially available automotivewaterborne base coat/clear coat system and baked 20 minutes at 275degrees F. Adhesion was then checked with a 3 mm crosshatch of both theprimer to electrocoat only area and the top coated area of the panel.Excellent adhesion was noted in both areas of the panel. The bottom halfof the panel was the chipped in a Q-Panel Gravelometer machine with 2pints of gravel at −20 degrees C. Excellent chip resistance was noted.Adhesion Ratings: Gravelometer Rating: GM8 Primer only   0 topcoat  1

Example 4 Paint Formulation with Polyester Dispersion

[0145] Preparation of Paint:

[0146] The dispersed polyester from Example 2 was formulated into aprimer as follows:

[0147] 1. A 201 gram aliquot of resin dispersion prepared as describedin Example 2 was placed in a one liter stainless steel mixing vessel

[0148] 2. 15 grams of butoxy ethanol and 26 grams of deionized waterwere then added to the resin dispersion

[0149] 3. A vertical disperser was then inserted

[0150] 4. 151 grams of TiO2 (R-920, DuPont) and 3 grams of Raven 16 wereadded under agitation.

[0151] 5. Approximately 300 grams of 3 mm glass beads were added to thevessel, and the mixture was dispersed at high speed for 30 minutes todisperse the pigment to a 7 Hegman.

[0152] 6. The mill was slowed to mixing speed, and the following letdown ingredients were added under slow agitation:

[0153] 106 grams of polyester dispersion

[0154] 56 grams of BL-3175

[0155] 5.4 grams of Cymel 303

[0156] 6.8 grams of Nacure 5528

[0157] 2.2 grams of DC-14

[0158] 7. After incorporation of these ingredients, the mixture wasfiltered through a 25 micron filter cone to remove the glass beads. ThepH is then adjusted to 8.2 to 8.5 with DMEA, and then reduced to 30-32seconds #4 Ford cup with deionized water.

[0159] The resulting paint had a calculated VOC of less than 2.0 poundsper gallon, and 53%, weight non-volatile.

[0160] Properties of the Paint:

[0161] The formulated paint was tested by spraying ontoelectrodeposition coated cold rolled steel panels. Film thickness of theprimer was 1.0 mil dry. The painted panel was flashed at roomtemperature for 5 minutes, and then flashed an additional 10 minutes ina 180 degrees F. oven. The painted panel was then baked 25 minutes at330 degrees F. The panel was the top coated with a commerciallyavailable automotive waterborne basecoat/clearcoat system and baked 30minutes at 250 degrees F.

[0162] Adhesion was then checked with a 3 mm crosshatch of the topcoated area of the panel. Excellent adhesion was noted on the panel. Thebottom half of the panel was then chipped in a Erichsen Chip testermachine with 1.0 kg of steel shot at room temperature. Excellent chipresistance was noted. Adhesion Rating: Erichsen Rating: 7 Topcoat  0

Example 5 Adhesion Rating Results

[0163] Procedures were conducted in accordance with SAE J400. SymbolElectrocoat Bake Primer Bake U/U 10 × 330 F. 25 × 275 F. U/T 10 × 330 F.25 × 330 F. U/H 10 × 330 F. 60 × 375 F. T/U 10 × 360 F. 25 × 275 F. T/T10 × 360 F. 25 × 330 F. T/H 10 × 360 F. 60 × 375 F. H/U 10 × 390 F. 25 ×275 F. H/T 10 × 390 F. 25 × 330 F. H/H 10 × 390 F. 60 × 375 F.

[0164] Polyester Hydroxyl Type Number U/U U/T U/O T/U T/T T/O O/U O/TO/O NPG 118 9/4 3/4 5/9 9/8 9/8 1/1 7/4 1/3 0/1 NPG/HDO 73 1/2 0/1 0/03/1 1/1 0/1 0/1 0/1 0/1 NPG 55 0/0 0/1 3/0 0/1 0/1 0/0 0/1 0/1 0/1

Example 6 Chip Rating Results

[0165] Procedures were conducted in accordance with ASTM D3359. 2 pintPolyester Hydroxyl chip 2 pint 3 pint 3 pint Type Number no. chip sizechip no. chip size comment NPG 118 5 B 4 rating B lower end of standardrating hydroxyl range (100-200) BEPD 110 4 B 3 rating B lower end ofstandard rating hydroxyl range (100-200) NPG/HDO 117 5 B 3 rating Blower end of standard rating hydroxyl range (100-200) BEPD 117 4 B 4rating B lower end of standard rating hydroxyl range (100-200) NPG/BEP66 5 A 4 rating A target range-lower than rating average NPG/HDO 73 5 A4 rating A target range-lower than rating average NPG/BEP 72 5 A 4rating A target range-lower than rating average NPG 55 5 A 4 rating Atarget range-lower than rating average BEPD 65 5 A 4 rating A targetrange-lower than rating average NPG 38 5 A 4 rating A extremely lowhydroxyl rating

[0166] Numerous modifications and variations in practice of theinvention are expected to occur to those skilled in the art uponconsideration of the foregoing detailed description of the invention.Consequently, such modifications and variations are intended to beincluded within the scope of the following claims.

What is claimed is:
 1. A polymeric vehicle comprising an aqueousdispersion of a polyester salt, wherein the polyester salt is a residueof a polyester having an acid value of at least 30, a number averagemolecular weight of at least 1500 and a hydroxyl value of not more than90, the aqueous dispersion effective for providing the polymeric vehiclewith less than about 5 weight percent organic solvent.
 2. The polymericvehicle as recited in claim 1 wherein the polyester salt is the residueof a polyester having an acid value of from about 40 to about 50 and ahydroxyl value of from about 90 to about 50 and a number averagemolecular weight of from about 1500 to about
 2800. 3. The polymericvehicle as recited in claim 2 wherein the polyester salt in the aqueousdispersion has a particle size of less than 400 nm.
 4. The polymericvehicle as recited in claim 3 wherein the polymeric vehicle is effectivefor providing a cured primer coating composition film, the primercoating composition film, when part of a multilayer coating having atleast two layers inclusive of the primer film effective for providingthe multilayer paint coating with a two pint chip number rating of atleast about 5 and a two pint chip size of at least about A.
 5. Thepolymeric vehicle as recited in claim 2 wherein the polyester includes—COOH groups which may be neutralized to form a water dispersible salt.6. The polymeric vehicle as recited in claim 1 wherein the polyesterincludes —COOH groups which may be neutralized to form a waterdispersible salt.
 7. The polymeric vehicle as recited in claim 3 whereinthe polymeric vehicle further includes a cross linker selected from thegroup consisting of an amino resin, an isocyanate compound and mixturesthereof.
 8. An aqueous polymer dispersion formed by a processcomprising: forming a polyester having sufficient —COOH groups toprovide the polyester with an acid value of from about 30 to about 50, anumber average molecular weight of about 1500 to about 2800 and ahydroxyl number of from about 50 to about 90, mixing the polyester in anorganic hydrophilic solvent, wherein the polyester polymer has asolubility in the hydrophilic solvent of at least about 50 weightpercent, and the organic hydrophilic solvent has a solubility in waterof at least about 5 weight percent; neutralizing at least about 30percent of the ionizable groups of the polyester with an amount ofneutralizer effective to form a solution of neutralized polymer salt;mixing the solution of neutralized polyester salt with water to form ablend of water/organic solvent/neutralized polyester; and stripping theorganic from the blend of water/organic solvent/neutralized polyesterblend at not more than about 65° C. to form a dispersion of neutralizedpolyester salt in water, the dispersion having a viscosity of less thanabout 10 poise at a temperature of about 25° C.
 9. The aqueous polymerdispersion according to claims 8 wherein the neutralizer is selectedfrom the group consisting of ammonia, triethanol amine,2-amino-2-methyl-1-propanol, and dimethyl ethanol amine.
 10. The aqueouspolymer dispersion according to claim 8 wherein water is added to thesolution of the neutralized polyester in an amount effective to providean initial ratio of organic solvent to water of from about 0.15 to about0.45.
 11. The aqueous polymer dispersion according to claim 10 whereinorganic solvent is removed without an inversion.
 12. The aqueous polymerdispersion according to claim 8 wherein the process is effective forproviding the polyester salt in the aqueous dispersion with a meanparticle size of not more than about 400 nm.
 13. An aqueous dispersionof a polyester salt, wherein the polyester salt is the residue of apolyester having a number average molecular weight in the range of fromabout 1500 to about 2800 and a hydroxyl value of from about 90 to about50, and an acid value of from about 40 to about 50, the polyester having—COOH groups which are neutralizeable to form a water dispersiblepolyester salt.
 14. An aqueous dispersion of a polyester salt accordingto claim 13 wherein the polyester has a number average molecular weightof about 1500 and a hydroxyl value of about
 90. 15. An aqueousdispersion of a polyester salt according to claim 13 wherein thepolyester has a number average molecular weight of about 2800 and ahydroxyl value of about
 50. 16. A multilayer paint coating having a twopint chip number rating of at least about 5 and a two pint chip size ofat least about A which is provided by application of a polymeric vehicleto a substrate, the polymeric vehicle comprising an aqueous dispersionof a polyester salt, wherein the polyester salt is the residue of apolyester having a number average molecular weight of at least 1500 anda hydroxyl value of not more than 90.